1. Field of the Invention
The present invention relates to an electrophotographic image forming method and an electrophotographic image forming apparatus.
2. Discussion of the Background
Recently, a need exists for an electrophotographic image forming method by which high quality images can be produced at a high speed. In order to produce high quality images fixation of toner images is an important factor. Specifically, when high speed image formation is performed, the fixing property of fixed toner images deteriorates. Therefore, it is a problem to be solved that toner images are sufficiently fixed even at a high speed image forming (fixing) speed.
There is a technique in that the fixing temperature is increased as the image forming speed is increased in order to prevent deterioration of the fixing property of toner images. However, the technique causes other problems such that the inner temperature of the image forming apparatus increases, resulting in deterioration of the image forming materials such as toners, and photoreceptors; the life of the fixing members shortens; and a large amount of energy is consumed. Namely, the technique is not satisfactory. Therefore, a need exists for a toner which can be well fixed in a small amount of energy even when high speed image formation is performed.
Various attempts have been made to develop such a toner. For example, techniques in that the thermal properties of binder resins used for toner is controlled have been investigated. Specifically, published unexamined Japanese patent applications Nos. (hereinafter referred to as JP-As) 60-90344, 64-15755, 02-82267, 03-229264, 03-41470, and 11-305486 have disclosed to use polyester resins as binder resins instead of styrene-acrylic resins which have been conventionally used as binder resins. This is because polyester resins are superior to styrene-acrylic resins with respect to low temperature fixability and high temperature preservability.
JP-A 62-63940 discloses a toner including a specific crystalline non-olefin polymer, which can be sharply melted at the glass transition temperature thereof, as one of binder resins. JP-As 11-249339 and 2001-222138 have disclosed to use a crystalline polyester resin having a sharp melting property as one of binder resins. In addition, JP-A 2002-214833 discloses to use a combination of a crystalline polyester resin and a non-crystalline polyester resin as binder resins, which form a phase separation structure (i.e. island-sea structure) and which include tetrahydrofuran-soluble components having a specific differential scanning calorimetry (DSC) curve such that a maximum endothermic peak is observed at a specific temperature to impart good combination of low temperature fixability and high temperature preservability to the toner.
On the other hand, fixing devices often cause problems in that when image fixation is performed, the surface of a fixing member is contaminated with toner particles, which are transferred from toner images to be fixed on a receiving material sheet, and thereby the toner particles are re-transferred to the sheet or another sheet, thereby soiling images, or a receiving material sheet is wound around the fixing member by being affixed to the melted toner particles on the fixing member, resulting in occurrence of a jamming problem. In attempting to prevent such problems, techniques in that a releasing oil is applied to a fixing member have been proposed and used.
Recently, toner including a release agent is used. However, even when such toner is used for high speed image forming apparatus, it is necessary to use a fixing device equipped with an oil applicator for the apparatus although the coating amount of oil can be decreased compared to a case where toner including no release agent is used.
Various oil applicators have been disclosed. For example, oil application devices including an oil application roller having a heat resistant felt or a porous layer on the surface thereof, which is soaked with an oil, is pressed to a fixing member to apply the oil thereto have been proposed and used. However, when the oil application devices are used for high speed image forming apparatus, toner images on a receiving material cannot be well fixed due to insufficient fixation energy although the fixing member has good releasability from the toner images, resulting in prevention of occurrence of an offset problem.
Because of these reasons, a need exists for an image forming method and apparatus by which high quality images having good fixing property can be formed using a toner including a release agent and a fixing device having an oil applicator.